This invention relates to wireless networks, in particular to wireless networks in enclosed environments such as, for example, a home or office.
With the growing use of computer systems such as PCs within office or working environments provision of suitable conduits for the necessary cabling, in particular network cables, has become increasingly difficult. Furthermore, working environments are often altered such as rearranging an open-plan office, or reorganising partitions in an environment having conventional offices. In production facilities the increasing reliance on information technology makes computer networks essentialxe2x80x94yet, again, the cabling requirements pose significant difficulties.
With the rapid increase in the number of multimedia appliances (e.g. video equipment, home theatres, PCs, etc) being used in the home, there is also a growing requirement for a network for controlling and connecting such multimedia appliances which is not unsightly. Such networks need to be easy to install, easy to set up, easy to maintain and easy to use. The required network should link the above-described home, office or production appliances to each other and to wide area networks such as, for example, the Internet, video servers or other communications media, via a central server.
It has been proposed to use wireless communication media for such networks which offer advantages over wired systems in that they are easy to physically install and such systems are known for use in the control of television systems, communication of audio signals to remote speakers, communication between a PC and a printer, and the like.
In such a wireless network, individual apparatus are linked to each other and/or a central server system by wireless communications and each apparatus can typically transmit and receive wireless signals. Such a system may be termed a wireless LAN
However, there is a need to transmit digital data at every increasing data rates for multimedia information. The carrier frequencies required for such data rates are at least in the Gigahertz (GHz) range. At carrier frequencies in the Gigahertz range, communication systems suffer from the effects of reflections and attenuation from walls, windows and partitions, etc, typically found in work or home environments which can affect the Bit Error Rate (BER) performance of the system, thereby resulting in retransmission of data and an undesirable or even unacceptable reduction in data throughout. A source of poor BER performance at so-called medium carrier frequencies, i.e. in the range about 2 to 15 GHz, is that reflections manifest themselves as sources of multipath propagation that can result in inter-symbol interference at a receiving apparatus. Additionally, many applications involve compressed video or audio and it is preferable for the data to arrive at the receiver in the correct order to avoid excessive buffering and delays, and/or complex error correction algorithms and processing circuitry to compensate for any lost or corrupted data.
In the case of medium frequency systems (2 to 15 GHz carrier frequencies), multipath signals at the receiver give rise to inter-symbol interference in the demodulated data stream. To reduce the effect of such multipath propagation, the system must utilise complex echo cancellation or equalisation techniques. In this application, the steerable antenna can be used to amplify the gain of the primary signal whilst attenuating the multipath signals with nulls, thus simplifying the echo cancelling requirements. Alternatively, in the case of a CDMA system where one wishes to increase the signal received from multipath signals at the input to the RAKE receiver, the steerable antenna can be used to increase the strength of the signal received at the RAKE receiver.
At very high carrier frequencies, i.e. in the range about 15 to 60 GHz, the attenuation due to walls or partitions, etc, gives rise to significant received signal power level problems, where the transmitting apparatus and receiving apparatus are not in line of sight. If there is excessive BER, the system performance and overall quality of audio-visual degrades due to the need for retransmission of erroneous data. At such high frequencies, it may be possible to only detect a signal resulting from a reflection from a partition or wall.
For very high carrier frequencies, simulation results show that the amount of diffusion of power through partitions and doors, etc is low and is highly dependent upon the material and construction of partitions and the position of furniture, for example. In addition, small changes in the-environment affect the propagation of RF within the building. At these frequencies (15 to 60 GHz), a reasonable level of reflection from walls and/or internal or external objects (via doors, windows, and the like) in the environment can be anticipated as disclosed in publication xe2x80x9cPredicted HIPERLAN coverage and outage performance at 5.2 and 17 GHz using indoor 3D Ray tracing techniquesxe2x80x9d A R Nix et al, Wireless Communications Journal 1996.
Experimental results published in the literature, i.e. xe2x80x9cInvestigation of the Effects of Antenna Directivity on Wireless Indoor Communication Systems at 60 GHzxe2x80x9d by M R Williams et al, Proceedings of Workshop on Wireless Multimedia Communication Systems, Kings College, June 97, show that the bit error rate (BER) performance of a wireless communication system can be dramatically improved by the use of highly directional antennas. In theory, optimum performance can be achieved if the beams of both the transmitter and receiver are aligned on the line of sight and the angle of spread of the beams are minimised in order to reduce reflections and multipath propagation. It is apparent that, as the beams narrow, a concomitant accuracy of beam alignment must be maintained. Also, the narrower the beam, the more rapid the degradation in performance if the beam goes out of alignment.
In the majority of home and work environments, it is highly improbable that line of sight communication between all appliances can be achieved, especially to those appliances that are ergonomically located. In a practical situation, in order to provide communication at such high frequencies, reliance upon reflections within the building or via windows to and from external objects or diffusion or diffraction through and under partitions and doors would be required in addition to, or alternatively to, line of sight, where possible, to maximise the likelihood of obtaining signal power levels suitable for communication.
In order to reduce the problems with unwanted reflections and poor signal strength due to attenuation through walls or partitions, etc, it is desirable to provide antennas which are directional so that they transmit and receive in narrow directions only. Thus, by properly aligning the directional antennas, the transmission problems giving rise to poor BER may be mitigated.
Although it is possible to create a computer simulation of the effects of a building on the propagation of a radio signal and to define the optimum position of transmitting and receiving antennas, and their direction of propagation, it is an impractical solution since the environment (location of obstructions, number and location of equipment, etc) often changes. Such a wireless home or work network is difficult to set up and maintain without continual adjustment and therefore further computer simulation.
Such an approach relies upon complex simulation of the transmission characteristics of the environment taking into account an accurate geometric map of the environment, the physical properties of materials comprising partitions and the effect of reflections from objects that are exterior of the building (reference xe2x80x9cA Ray Tracing for Microcellular Wideband Propagation Modellingxe2x80x9d, G E Athanasiadou et al, IEEE, VTC, Chicago, 1995). Any modification to the environment leads to either a requirement for a new simulation and repositioning of antennas or the possible degradation of the performance of the network.
In accordance with a first aspect of the present invention, there is provided an antenna network system, comprising:
a server including a transmitter and an antenna;
a client including a receiver and a steerable antenna;
a control path independently operable of a primary wireless communications channel between said antennas, the control path for communicating control data between said server and client; and
server control means responsive to signal quality data communicated via said control path for steering said client antenna in a direction for optimising signal quality of communications transmitted between said antennas.
In accordance with a second aspect of the present invention, there-is provided a method for automatically calibrating an antenna network system including a server antenna and steerable client antenna, the method comprising:
transmitting a wireless signal from said server antenna;
receiving said wireless signal at said client antenna for each one of a plurality of directions for said client antenna;
noting received signal quality for respective client antenna directions; and
steering said client antenna in a direction for optimising said received signal quality.
In a preferred embodiment, the method comprises steering the server antenna in a plurality of directions, and receiving the wireless signal at the client antenna for each one of the plurality of directions of the client antenna for each of the plurality of directions for the server antenna. Thus, it is possible to build up measurements of the received signal quality for each combination of client and server antenna directions. Having the control path independent of the primary wireless communications channel means that control data can be exchanged even if there is a breakdown in the primary communications channel.
Preferably, data corresponding to the noted received signal quality for respective client antenna directions is communicated to the server over the control path at a lower data rate than the data rate for the primary wireless channel. Typically, such data comprises respective received signal quality values and corresponding client antenna direction information. By having the control path operable at a low data rate, low carrier frequencies may be used and thus suitable communications media for such low carrier frequencies may be utilised. Suitable low carrier frequencies would be lower than about 1 GHz.
Suitably, the server forms a database of the data forwarded to it from the client antenna over the control path and searches said database to identify a client antenna direction yielding optimum signal quality. The method further comprises communicating control signals over the control path to the client antenna for steering the client antenna in the identified optimum direction.
Optionally, the method further comprises including in the database data corresponding to the server antenna direction for each of the data recorded for the client antenna, searching for a server antenna direction and client antenna direction pair yielding optimum signal quality, and steering the server antenna and the client in respective directions for that optimum signal quality. Steering of the client antenna being achieved by forwarding suitable control signals over the control path.
Preferably, the control path comprises a power supply line including a suitable modem/s, telephone system, cable system or cordless telephone system, for example the DECT telephone system. One or other of such systems are particularly advantageous, since they can be operated at relatively low frequencies and/or data rates and can provide substantially continuous communication for control signals between the server and the client. Optionally, the control path is wireless, and may even be transmitted from the server and/or client antennas. However, since the data rate and hence carrier frequency is substantially lower than the data rate for the primary wireless communications channel, the propagation over the wireless control path is more robust, and does not suffer from the problems experienced for the primary channel.
Suitably, the client and/or the server comprise signal processing circuitry for receiving and transmitting control data between them over the control path.
The client may also comprise signal processing circuitry for determining the quality of a signal received from the server via respective client and server antennas.
The client signal processing circuitry may be operable to steer the client antenna in accordance with control signals received from the server via a control path.
Advantageously, the server antenna is a steerable antenna, which provides for further optimisation of received signal quality by suitably directing-the server antenna. Typically, the server signal processing circuitry is operable to steer the server antenna in a direction in accordance with the signal quality data communicated to it from the client via the control path.
Either one or both of the server and client antennas may be operable to form a complex antenna beam pattern in accordance with respective signals communicated by the control path. This advantageously provides an antenna beam pattern suitable for receiving and optimising signals via multipath propagation.
The server can transmit control data to the client for forming beam patterns and steering the antenna, such that all the processing and control is performed in the server.
In accordance with embodiments of the present invention, there is provided a system which enables transmission of bidirectional data using high carrier frequencies (in the range of 2 to 60 GHz) between a wireless server and wireless client appliances. The system enables optimisation of the available bandwidth of the network by using directional antennas to improve BER. In addition, the system improves flexibility in terms of the physical location of the transmitter and receivers. The receivers can comprise or feed any number of client appliances, such as TV, camcorder, VCR, satellite receivers, DVD, DAB, interactive playstations, personal computers, printers, web TVs, virtual reality shopping centres, educational terminals, wireless books, etc. Each appliance is effectively connected to any other appliance via the wireless LAN to the server. The server may be connected to the Internet service supplier via a high speed connection, in order to provide network access to such services for the above-mentioned client appliances.
Embodiments of the present invention, at the above-described medium carrier frequencies (in the range of 2 to 15 GHz), enable identification of the source of maximum RF carrier power arriving at the receiver(s) as a result reflections and/or diffusion as well. as line of sight. By correctly aligning the beam of the antenna of the appliance and/or the server in the direction of maximum power, not only is BER improved due to the improved signal to noise (S/N) ratio at the receiver(s), but also the effective power received from multipath propagation may be improved for CDMA systems and conversely reduced for TDMA or FDMA systems. The overall result is an improvement in BER performance of the system and/or ability to greatly simplify the equaliser of the receiver and/or the ability to increase the data rate of the system due to the reduction in inter-symbol interference.
With embodiments of the present invention, the sources of maximum RF power arriving at the receiver(s) as a result of reflections and/or diffusion can be identified. Also, the optimum alignment of the beams of the transmitter and/or receiver(s) can be calculated to either limit inter-symbol interference due to multipath propagation or to increase the S/N radio by correct beam alignment. Performance (i.e. BER) of the receiver(s) may be optimised, leading to an improvement in quality for transmission of real time information such as multimedia data. Alternatively, the system can accommodate a larger number of receivers within the LAN or a higher effective data rate for a given carrier frequency or if the equipment is battery operated (e.g. wireless electronic book or PDA) one can reduce the power of the transmitter/receiver for a given performance giving rise to an increase in battery life.
To communicate the status of beam alignment between the wireless client appliance and the wireless server, an alternate communication path for transmitting control and status information is established. The transmission media chosen for the control signal path is such that bidirectional control communications may be maintained even if the main transmitting apparatus/receiving apparatus beams are not aligned (i.e. the main medium or high carrier frequency system is not able to transmit and receive data). Examples of technology that could be used for the control path over a short distance are low frequency wireless telephone (2 GHz carrier or below), modulation of the mains power network, a conventional modem connected to the telephone network, DECT wireless systems or even using a temporary wireline connection.
By utilising an alternate transmission medium/system for the transmission of control and status information, the set up of the system can be automated and effectively one can achieve a xe2x80x9cplug and playxe2x80x9d network.
Reliance is placed upon the use of steerable multiple element antennas to transmit/receive information in the home or office network. Multiple element steerable antennas have been used in military applications for many years. Using well-known digital signal processing techniques, the amplitude and phase of the antenna elements of the receiver are adjusted to create a signal beam of a maximum gain. By adjusting the relative phases and amplitudes of the receiver(s) antenna elements, the signal beam is swept in both horizontal directions and subsequently in elevation while measuring the received carrier signal strength. The resultant variation in strength of the received signal creates a three-dimensional map of the transmission characteristics of the environment for a given direction of the transmitted beam. The direction of the transmitted beam is then adjusted by an incremental angle and the procedures are repeated. Using the resulting maps of signal strengths at the receiver(s) for all transmitted beam directions, the spatial gain of the transmitting and receiving antenna(s) are then adjusted for optimised signal reception at the specific carrier frequency. By this invention, there is a combination of the use of a lower frequency control path with the beam sweeping technique to automatically map the transmission characteristics of a home or office environment. Using the resultant map, the spatial gain of the antennas is arranged for optimum transmission. The control of the spatial gain is enacted by transmitting via the control path of the necessary data for optimum configuration of the antennas and their elements.
The control information relayed between the wireless server and the wireless client appliance includes (as a minimum) the carrier frequency in use and the direction of the antenna beams at a given point in time and the resultant measurement of receiver RF power. Optionally, the elevation and/or width of the antenna beams may also be communicated. The control information for each appliance is stored in a temporary memory for future calculations. By comparing the stored results of signal strength of the various orientations of the transmitter and receiver beams, the server can identify the optimum direction in which the beams of the transmitter and receiver should be oriented to maximise the S/N ratio and the achieve optimum performance, in particular in terms of BER. Finally, at the end of the calibration procedure, the server sets the optimum beam configuration at the client and server (for a steerable server antenna) transmitter and receiver for respective transmitter/receiver communication by communicating the preferred settings to the wireless client appliance via the control path.
The calibration procedure can be reenacted on a periodic basis or when the performance of the communication system degrades below a preset limit or when a new wireless client appliance is added to the network.
The process can be repeated for different carrier frequencies or for different azimuth to again select the beam configuration and carrier frequency for optimum reception at the receivers.
By virtue of the principle of reciprocity, the optimum antenna configuration is the same for both the wireless server and a wireless client appliance in either transmit or receive mode.
Optionally, the process can also be repeated for uplink (client appliances to server) transmission of information by treating the client appliance as the transmitter and the server as the receiver.
The system can also be used to provide feedback to the user as to the optimum placement of transmitting and receiving antennas. In many instances, it would be possible to further improve the performance of the network by utilising the information stored in the temporary memory regarding the variation in RF power at the receivers to advise of modifications in the physical location of the receivers. For example, if the maximum powers are recorded in the nxe2x88x921, nth and n+1 sectors, then the user could be provided with an indication that moving the antenna in the direction of the nth sector and restarting the calibration routine could further improve performance. This option would be of great benefit if the power received in the sector of highest power (nth) is below a preset limit that is deemed to be necessary to ensure adequate BER performance of the system.
Particular and preferred aspects of the invention are set out in the accompanying independent claims. Combinations of features from the dependent and/or independent claims may be combined as appropriate and not merely as set out in the claims.